- Joined
- Jul 20, 2004
How much is Too Much?
By our very own rebturtle.
generally, he got it right.
but allso there are a few things that are misleading and prictical knowledge/vs code theory issues.
1. ampacity shall not be less than overcurrent except for motor loads.
basically, IN THEORY the scary pictures of a modern home burnt before it was finished due to overload are either inexcusable electrical work (probably a lost licence, and a lawsuit in there somewhere) or faulty overcurrent devices.
huh? -you say?
basically, breakers exist to protect the wire, and the wire only. breakers dont care if your stuff dies, they just keep the wires from burning and setting fires.
most all the wire in new homes is rated to 90C
the breaker/fuse will ALLWAYS trip well before the wire melts by design (in theory) if it doesnt, the wire was undersized, or the breaker was faulty.
considering the high prices of copper, i am not surprised to see a fire or two if someone cheaped out.
2. wires and capacity are NOT the problem for most overclockers, assuming properly sized wire/proper overcurrent.
its all insulation.
remember when i said modern wire was rated for 90C?
it is!
but older homes have as little as 60C ratings (i done that on my northwood kids) , when they were built 40 or 70 years ago. how many times have those ratings been exceeded over the years? how much has that wire degraded?
chances are, its pretty close to dust if its "old" . thats fine with normal loads and if you dont disturb the wires... but anything can happen over the years, and this is why we now use 90C wire....
3. ambient and load temperature:
(sounds fimilliar, huh?)
wire is rated for ambient and load temperatures too!
the MODERN base for ambient temperatures is 86F (nec2005 310.16)
once you exceed that the wire is AUTOMATICALLY DE-RATED.
so your #12, 20 amp circut for your killowatt prescott that runs across the attic on a hot day? in an old house? your 60C wire in a 130F attic is only good for 8.2 amps - 984W, on a good day in perfect condition.
your killowatt prescott just might burn your house down if your overcurrent device dosnt trip...in this scenario.
bump it up to a 140F attic (common in the south) and youve just departed the temperatre derating factors for 60C wire in 310.16. -youre off the charts.
why is this important?
because if your insulation melts/catches fire, and you assume that could only be possible if your overcurrent device is asleep at the switch, youve got an instant fire, or a potential short. same difference.
randy, your dryer is tripped, btw...
By our very own rebturtle.
generally, he got it right.
but allso there are a few things that are misleading and prictical knowledge/vs code theory issues.
1. ampacity shall not be less than overcurrent except for motor loads.
basically, IN THEORY the scary pictures of a modern home burnt before it was finished due to overload are either inexcusable electrical work (probably a lost licence, and a lawsuit in there somewhere) or faulty overcurrent devices.
huh? -you say?
basically, breakers exist to protect the wire, and the wire only. breakers dont care if your stuff dies, they just keep the wires from burning and setting fires.
most all the wire in new homes is rated to 90C
the breaker/fuse will ALLWAYS trip well before the wire melts by design (in theory) if it doesnt, the wire was undersized, or the breaker was faulty.
considering the high prices of copper, i am not surprised to see a fire or two if someone cheaped out.
2. wires and capacity are NOT the problem for most overclockers, assuming properly sized wire/proper overcurrent.
its all insulation.
remember when i said modern wire was rated for 90C?
it is!
but older homes have as little as 60C ratings (i done that on my northwood kids) , when they were built 40 or 70 years ago. how many times have those ratings been exceeded over the years? how much has that wire degraded?
chances are, its pretty close to dust if its "old" . thats fine with normal loads and if you dont disturb the wires... but anything can happen over the years, and this is why we now use 90C wire....
3. ambient and load temperature:
(sounds fimilliar, huh?)
wire is rated for ambient and load temperatures too!
the MODERN base for ambient temperatures is 86F (nec2005 310.16)
once you exceed that the wire is AUTOMATICALLY DE-RATED.
so your #12, 20 amp circut for your killowatt prescott that runs across the attic on a hot day? in an old house? your 60C wire in a 130F attic is only good for 8.2 amps - 984W, on a good day in perfect condition.
your killowatt prescott just might burn your house down if your overcurrent device dosnt trip...in this scenario.
bump it up to a 140F attic (common in the south) and youve just departed the temperatre derating factors for 60C wire in 310.16. -youre off the charts.
why is this important?
because if your insulation melts/catches fire, and you assume that could only be possible if your overcurrent device is asleep at the switch, youve got an instant fire, or a potential short. same difference.
randy, your dryer is tripped, btw...
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